rfc7: break long test expressions to one per line

Problem: We've adopted a defacto guideline that long test expressions
connected by "AND" or "OR" operators should be broken to one test
expression per line.  This is not documented.

Add this to RFC 7.

spec_7.rst

@@ -86,6 +86,24 @@ to one parameter per line, at the same indent level.  Example:
                   FLUX_NODEID_ANY,
                   FLUX_RPC_RESPONSE);
 
+10. Long test expressions connected by "AND" or "OR" operators SHOULD
+be broken to one test expression per line at the same indent level.
+Example:
+
+  .. code-block:: c
+
+    if (out->type == MY_EXPECTED_TYPE
+        && (out->bytes > MIN_BYTES
+            && out->bytes <= MAX_BYTES)) {
+        ...
+    }
+
+  .. code-block:: c
+
+    if (flux_event_subscribe (h, "event.foo") < 0
+        || flux_event_subscribe (h, "event.bar") < 0) {
+        ...
+    }
 
 Variable Names
 ==============